Ion-producing mechanism for calutrons



Dec. 24, 1963 w. A. BELL, JR., ETAL 3,115,575

ION-PRODUCING MECHANISM FOR CALUTRONS Filed Oct. 31 1961 2 Sheets-Sheet 1 INVENTORS. William A. Bell, Jr. Willis K. Prafer ATTORNEY Dec. 24, 1963 W. A. BELL, JR.. ETAL ION-PRODUCING MECHANISM FOR CALUTRONS Filed Oct. 31, 1961 2 Sheets-Sheet 2 aw W m m8 V1. A .m m M f m f l 31 24 2 9 5 8 2 5 3 O 3 Y Willis K. Prafer ATTORNEY United States Patent Ofiice 3,115,575 Patented Dec. 2%, 19%,?

ION-PRODUCING MECHANEM FDli CALUTRDNS William A. Bell, Jr., Oak Ridge, and Willis K. Prater,

Knoxville, Tenn, assignors to the United States of America as represented by the United States Atomic Energy Commission Filed Oct. 31, 196i, Ser. No. 149,131 3 Claims. (Cl. 256-413) The present invention relates to ion-producing mechanisms, and more particularly to an improved ion-producing mechanism for the electromagnetically operated equipment known as calutrons for the separation of isotopes or elements.

It has been shown that isotopes of many chemical elements can be separated and the desired elements enriched in the electromagnetic mass spectrometer known as the calutron, described in the E. 0. Lawrence Patent No. 2,709,222. In the calutron, as described in the patent, there is provided an ion-producing means wherein a feed of charge material is converted into ions for subsequent acceleration through a magnetic field and separation into the respective masses of the isotopes presents in the charge material. Since most charge materials are solids, the charge must first be heated in a vaporizer or oven to produce a charge vapor. Vapor from the vaporizer or oven passes to an arc chamber where a stream of electrons (commonly called the arc) is passed through these vapors, ionizing them for subsequent acceleration. Although the heat caused by this ionizing arc may be sufficient to pro duce vaporization of some elements, the vaporization and ionization areas are normally separated so that the temperature, particularly of the vaporizing oven, can be carefully controlled and so that operating conditions of the arc can be modified for optimum performance without influencing the temperature of the oven.

In production calutrons used in the prior art, the ionproducing mechanism has been constructed in two distinct sections. The oven unit at the rear of the mechanism is normally a casting of a copper alloy containing therein the necessary heating elements and a cavity to accommodate a bottle containing the charge material. Communicating with vapor exit openings in the oven unit are mating openings leading into the ionization region (commonly referred to as arc chamber). The are chamber unit is normally fabricated of carbon and inserted into a copper alloy casting provided with appropriate heating means. These components are all mounted on a frame in proper alignment with respect to the magnetic field, cathode filament and accelerating electrodes.

This conventional construction of ion-producing mechanisms has a number of disadvantages. Since it is possible to operate only within some limited temperature range (e.g., 350-700 C.) with any one model of the prior art ion-producing mechanism, one disadvantage is that any one ion-producing mechanism cannot be used in the separation of the isotopes of many different elements where the operating temperatures vary widely for the different elements.

Perhaps a greater disadvantage of the prior art ionproducing mechanism is the length of time required for assembly or disassembly of a mechanism; particularly the time required to replace any components thereof, if failure occurs during a production run. Another difficulty is the considerable labor and time required for washing and decontamination of the mechanism. The extent of this handling for decontamination is increased when the charge materials contain toxic, chemically reactive, or radioactive constituents. When toxic and chemically reactive charge material were involved, prior art mechanisms had to be completely dismantled and cleaned, often with remote handling tools, and then reassembled before reuse.

In the case of radioactive charge materials, prior art mechanisms usually could not be reused. In addition, the prior ion producers were so arranged that they caused during operation extensive contamination of the other components of the calutron.

With knowledge of these and many other deficiencies of prior art ion-producing mechanisms, applicants have as an object of their invention to provide an ion-producing mechanism of unitized construction for calutrons that substantially reduces the time for assembly and installation.

It is another object of the present invention to provide an ion-producing mechanism of unitized construction which, when used with reactive charge material, substantially reduces contamination of other calutron components during operation.

It is a further object of the subject invention to provide an ionproducing mechanism that, with only minor modifications, can be utilized with charge material that vaporizes from room temperature up to approximately 1200 centigrade.

It is a further object of this invention to provide an ionproducing mechanism wherein the temperature and vapor pressure can be more closely controlled than in those of the prior art.

It is a further object to provide an ion-producing mechanism that can be more conveniently handled when toxic, chemically reactive, or radioactive charge materials are utilized.

It is further an object of the subject invention to provide an ion-producing mechanism more economical to manufacture, install, maintain and operate.

Other objects and advantages of the present invention will become apparent from the following detailed description of a preferred embodiment thereof, when read in connection with the appended drawings, in which:

FIGURE 1 is a perspective view of the unitized enclosure of our ion-producing mechanism mounted on a water-cooled support member.

FIGURE 2 is a cross-section of the same unitized enclosure taken along line 2-2 of FIGURE 3.

FIGURE 3 is a sectional plan view of the same enclosure, showing the oven section heater construction, taken along line 33 of FIGURE 5.

FIGURE 4 is a side view of the unitized enclosure showing heater terminals for both the arc chamber section and the oven section of the enclosure.

FIGURE 5 is a front view of the enclosure showing the ion exit slit and the heater terminals for the arc chamber section.

In accordance with our invention, we form the ionproducing mechanism in a single, unitized structure with the oven section and the arc chamber combined into one composite enclosure. This unitized enclosure is preassembled and then inserted in the remainder of the calutron source unit. In the calutron source unit, a watercooled support bracket provides the necessary alignment of the enclosure with respect to the cathode filament, magnetic field, and accelerating electrodes.

The unitized enclosure preferably comprises two sections: an ionization or are chamber section for ionization of the vapors from the charge material, and an oven section for heating and vaporizing the charge material to be ionized. Between these two sections of the enclosure is provided a vapor passageway for transmitting vapors from the oven section to the arc chamber section. The oven section comprises a large central cavity for the accommodation of a charge bottle and heaters adjacent two sides within the cavity for vaporizing the charge material in the charge bottle. The are chamber section of the enclosure comprises a central cavity which is divided by a perforated baflle into two regions; a vapor manifold region with an inlet passageway for the vapors, and an ionizing region for ionization of the vapors. Spaced equally from the central cavity are two heater cavities with heaters disposed therein. Ions from the ionizing region pass through an exit slit and are accelerated through the magnetic field of the calutron to a collection receiver.

In order to control the temperature gradient in the enclosure and between the two sections of the enclosure, thermal insulation is provided. In the oven section thermal insulation consisting of graphite sheets is disposed on all sides and both ends of the charge bottle. In the arc chamber section, thermal insulation is disposed in the heater cavities between the Walls of the cavity and the heaters. By using more or less thermal insulation it is possible to vary the temperature of the different sections of the enclosure. For higher internal temperatures, more insulation is used, and for lower temperature, less insulation is needed. Also, it is usually necessary to maintain the arc chamber section at a higher temperature than the oven section to prevent solidification of vapors entering the vapor manifold region. This temperature gradient can be maintained and controlled by varying the amount of thermal insulation, such as graphite, disposed between the two sections.

With reference to the drawings in detail, particularly FIGURE 2, the unitized enclosure is preferably divided into two sections, an arc chamber section 14 for ionization of the vapors from the charge material and an oven section 15 for heating and vaporizing the charge material to be ionized. These two sections may be me.- chined separately from rectangular graphite blocks and bolted together to form the unitized enclosure for the ionproducing mechanism.

The are chamber section 14- is formed with three principal cavities. First, a generally central longitudinal cavity 16 for the ionization of the charge vapors and which is provided with shoulders 17, 17 to accommodate a perforated graphite baffle 13. This bafile 13 extends the length of the central cavity 16 and separates the arc chamber section into two regions: the ionizing region and the vapor manifold region 19. Although the bafile Jill may be perforated in several different patterns, longitudinal perforations are preferred to provide adequate dispersion of the vapors entering the ionizing region. The central cavity 16 is bounded on the front by a slotted graphite insert defining an ion exit slit 2% fitted into the central cavity against second shoulders 21, 21 and held in place by plates 22, 22' (see FIGURES 4 and in tongue and groove fashion.

The ion exit slit insert 29, which has a U-shaped cross section, extends longitudinally the length of the central cavity 16 and by means of its extension into the central cavity provides improved heat transfer from the heaters 24, 24 to the ion exit slit to prevent solidification of vapors of elements or isotopes which may tend to con dense and solidify in the slit opening. When elements or isotopes are used which do not tend to condense and solidify in the slit opening, the slit insert may consist of a fiat graphite plate with a slot defining the ion exit slit fitted into the front of the arc chamber section in tongue and groove fashion and extending longitudinally the length of said section.

The vapor manifold region 19, which also extends the length of the central cavity, is provided with at least two drilled holes or vapor inlets to accommodate vaporexit nipples 33 extending from the charge bottle, hereinafter described. In addition to the central cavity, the arc chamber section 14 also contains two heater cavities 23, 23 spaced equally from the central cavity and extending almost the length of the arc chamber section from an open end to a closed end. Carbon heaters 24, 24 in ceramic supporting insulators 25, 25 and with appropriate terminals are inserted from the open end of the heater cavities 23, 23'. Thermal insulation in the form of a multiplicity of thin carbon sheets 26, 26' may be inserted, as shown, between the heaters 24-, 24 and the heater cavities 23, 23. Face plates 27, 27" are used to retain these components in the heater cavities.

The oven section 15 of the enclosure is machined with a large central U-shaped cavity 2&5 of rectangular cross section designed to accommodate a box-like charge bottle 29 for the heating and vaporization of charge material. This charge bottle 29 which is machined from graphite or stainless steel, depending upon the type of charge material to be vaporized and the temperatures required, is provided with a covered opening for insertion of charge material and at least two exits to accept the threaded vaporexit nipples 33. Carbon heaters 30, 30 in suitable ceramic supporting insulators 31, 31 are disposed adjacent two sides of the charge bottle 29 within the large central cavity 28 with appropriate terminals 32, 32 extending through slots in the rear of the large central cavity 28. Thermal insulation is provided, first by a box-like member 35, 35 machined preferably from carbon with an opening at the end nearest the arc chamber section 14. As in the arc chamber section, thermal insulation may be further provided by a multiplicity of thin carbon or graphite sheets 36 disposed on all sides within the large central cavity 2-8. Of especial importance is thermal insulation, of the type described, between the oven section 15 and the arc chamber section 14. This thermal insulation is drilled to accommodate the vapor-exit nipples 33 which extend from the charge bottle 29 to the vapor manifold region 19.

The heaters described for use in both sections of the ion-producing mechanism are machined from carbon or graphite, preferably in a zig-zag pattern, to provide the proper electrical resistance and optimum heater surface area for the particular element or isotope to be vaporized. Details of the heater design for the oven section are shown in FIGURE 3 in sectional plan view. It will be observed in FIGURE 3 that terminals 32, 32' from these heaters extend from the rear of the enclosure for connection to electrical sources.

Heater terminal details are shown in FIGURES 4 and 5. The oven section heater terminals 32, 32' extend from the rear of the unitized enclosure to be connected to the power source. The are chamber section heater terminals 37, 37' extend from the side of the enclosure with an extension 38 to the rear of the enclosure to be connected to the power source.

The oven section heaters 30, 30' are each connected in series and the arc chamber section heaters 24, 24 are each connected in series with the graphite unitized enclosure serving as a common ground terminal for both pairs of heaters.

In operation of our improved ion-producing mechanism, the charge material is placed in the charge bottle 29, which is tightly covered to prevent leakage into the oven section. The unitized enclosure is assembled, as described above, with the two sections bolted together. When the two sections are connected the vapor-exit nipples 33 from the charge bottle 29 extend into the vapor manifold region 19, and to prevent vapor leakage back into the oven section 15, threaded graphite nuts 34 are used to secure the vapor-exit nipples. Referring now to FIGURE 1, the assembled unitized enclosure 10 is then inserted in the calutron source unit, in a water-cooled support bracket 11, which provides the necessary alignment of the collimating slot 12 with respect to the cathode filament 13, and the alignment of the enclosure with respect to the magnetic field and accelerating electrodes. The collimating slot 12 is in the cathode side of the central cavity 16 to allow electrons from the filament 13 to enter therethrough and establish an are through the arc chamber. After the heater terminals are connected to a suitable power source, the calutron is operated in essentially the standard manner as described in the Lawrence patent. First an arc is struck through the arc chamber from the cathode filament to the opposite wall of the chamber, using a support gas, such as nitrogen,

for the arc, with the graphite enclosure serving as the anode. The charge material is then vaporized in the oven section and these vapors eventually support the arc and are ionized for subsequent acceleration.

Having described our invention, what is claimed is:

1. In a calutron, an improved ion-producing mechanism comprising a unitized graphite enclosure provided with an arc chamber at one end, a slotted graphite insert adjacent said chamber and defining an ion exit slit, a charge bottle, vapor manifold, and separate heaters for said charge bottle and said arc chamber, said enclosure defining both an arc chamber section and an oven section; said arc chamber section being provided with a central cavity for the ionization of the vapors from the charge material and two heater cavities of rectangular crosssection with first heaters disposed therein and spaced equally from said central cavity, said central cavity being subdivided by a perforated bafl le into a vapor manifold region and an ionizing region, said manifold region being adjacent one end of said oven section and communicating directly therewith; said oven section of said enclosure being provided with a large central cavity to accommodate said charge bottle, and second heaters disposed adjacent two sides of said charge bottle within said large central cavity, said charge bottle being provided with at least two vapor-exit nipples extending therefrom into said vapor manifold region of said arc chamber section, said unitized enclosure substantially reducing contamination of the other calutron components from any charge material reactive constituents.

2. In a calutron, an improved ion-producing mechanism for operating at temperatures up to about 1200 centigrade comprising a unitized graphite enclosure provided with an arc chamber at one end, a slotted graphite insert adjacent said chamber and defining an ion exit slit, a charge bottle, vapor manifold, and separate heaters for said charge bottle and said arc chamber, said enclosure defining both an arc chamber section and an oven section;

said arc chamber section being provided with a central cavity for the ionization of the vapors from the charge material and two heater cavities of rectangular crosssection with first heaters disposed therein and spaced equally from said central cavity, said heater cavities provided with thermal insulation sheets disposed between said first heaters and said heater cavities, said central cavity being subdivided by a perforated baffie into a vapor manifold region and an ionizing region, said manifold region being adjacent one end of said oven action and communicating directly therewith; said oven section of said enclosure being provided with a large central cavity to accommodate said charge bottle, second heaters disposed adjacent two sides of said charge bottle within said large central cavity, and thermal insulation sheets disposed on all sides and both ends of said large central cavity, said charge bottle being provided with at least two vapor-exit nipples extending therefrom through said thermal insulation sheets into said vapor manifold region of said are chamber section, said unitized enclosure substantially reducing contamination of the other calutron components from any charge material reactive constituents.

3. The improved ion producing mechanism of claim 2, wherein said charge bottle is shorter than said large central cavity of said oven section, thereby defining a recess between said charge bottle and said are chamber section and where said thermal insulation sheets include graphite plates removably disposed within said recess to control the thermal gradient between said oven section and said arc chamber section.

References Cited in the file of this patent UNITED STATES PATENTS 2,714,166 Starr July 26, 1955 2,715,682 Lawrence Aug. 16, 1955 2,715,683 Backus et al. Aug. 16, 1955 

1. IN A CALUTRON, AN IMPROVED ION-PRODUCING MECHANISM COMPRISING A UNITIZED GRAPHITE ENCLOSURE PROVIDED WITH AN ARC CHAMBER AT ONE END, A SLOTTED GRAPHITE INSERT ADJACENT SAID CHAMBER AND DEFINING AN ION EXIT SLIT, A CHARGE BOTTLE, VAPOR MANIFOLD, AND SEPARATE HEATERS FOR SAID CHARGE BOTTLE AND SAID ARC CHAMBER, SAID ENCLOSURE DEFINING BOTH AN ARC CHAMBER SECTION AND AN OVEN SECTION; SAID ARC CHAMBER SECTION BEING PROVIDED WITH A CENTRAL CAVITY FOR THE IONIZATION OF THE VAPORS FROM THE CHARGE MATERIAL AND TWO HEATER CAVITIES OF RECTANGULAR CROSSSECTION WITH FIRST HEATERS DISPOSED THEREIN AND SPACED EQUALLY FROM SAID CENTRAL CAVITY, SAID CENTRAL CAVITY BEING SUBDIVIDED BY A PERFORATED BAFFLE INTO A VAPOR MANIFOLD REGION AND AN IONIZING REGION, SAID MANIFOLD REGION BEING ADJACENT ONE END OF SAID OVEN SECTION AND COMMUNICATING DIRECTLY THEREWITH; SAID OVEN SECTION OF SAID ENCLOSURE BEING PROVIDED WITH A LARGE CENTRAL CAVITY TO ACCOMMODATE SAID CHARGE BOTTLE, AND SECOND HEATERS DISPOSED ADJACENT TWO SIDES OF SAID CHARGE BOTTLE WITHIN SAID LARGE CENTRAL CAVITY, SAID CHARGE BOTTLE BEING PROVIDED WITH AT LEAST TWO VAPOR-EXIT NIPPLES EXTENDING THEREFROM INTO SAID VAPOR MANIFOLD REGION OF SAID ARC CHAMBER SECTION, SAID UNITIZED ENCLOSURE SUBSTANTIALLY REDUCING CONTAMINATION OF THE OTHER CALUTRON COMPONENTS FROM ANY CHARGE MATERIAL REACTIVE CONSTITUENTS. 